1. Field of the Invention
The present invention relates to a dielectric ceramic material which can be obtained through low-temperature firing and also to a multilayer ceramic substrate using the dielectric ceramic material.
2. Description of Related Art
With the need of miniaturizing recently spread mobile communication equipment, such as portable phones, and portable communication terminals, the size reduction and performance increase of high-frequency circuit parts for use therein have been pursued.
In high-frequency circuit substrates, a conventional module including a printed substrate and a capacitor or inductor mounted on its surface has been increasingly replaced by a smaller size module consisting of multilayers of dielectric ceramic substrates each patterned with a capacitor or an inductor circuit.
The multilayer ceramic substrate is generally fabricated by providing multilayers of green sheets, such as glass ceramics, each carrying a predetermined circuit pattern formed by screen printing or the like, and firing them at a temperature of about 900° C.–about 1,000° C. A popular material used for the circuit pattern is high-conductivity and air-firable silver (Ag).
Where silver is used as a material for circuit pattern, a dielectric ceramic material for use in the multilayer ceramic substrate needs to be fired at a low temperature of about 900° C.–about 1,000° C., as described above, and generally comprises a low-firable glass ceramic material obtained by mixing a ceramic filler, e.g. alumina, and a glass (See, for example, Japanese Patent No. 3441924 and Japanese Patent Laying-Open No. Hei 10-120436). However, the higher glass loading lowers mechanical strength, which has been a problem.